|Publication number||US7049840 B1|
|Application number||US 09/302,576|
|Publication date||May 23, 2006|
|Filing date||Apr 30, 1999|
|Priority date||Mar 21, 1997|
|Also published as||US6025731|
|Publication number||09302576, 302576, US 7049840 B1, US 7049840B1, US-B1-7049840, US7049840 B1, US7049840B1|
|Inventors||David R. Hembree, Salman Akram, Warren M. Farnworth, Alan G. Wood, James M. Wark, Derek Gochnour|
|Original Assignee||Micron Technology, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (64), Non-Patent Citations (3), Classifications (9), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a division of patent application Ser. No. 08/821,468 filed Mar. 21, 1997 U.S. Pat. No. 6,025,731.
This invention relates generally to semiconductor manufacture and specifically to an interconnect for making electrical connections with a semiconductor die for testing or other purposes. This invention also relates to a method for fabricating the interconnect and to a system for testing dice that includes the interconnect.
During a semiconductor fabrication process semiconductor dice are formed on a wafer. Subsequent to the fabrication process the dice must be tested to evaluate the electrical characteristics of the integrated circuits formed on the dice. Tests for gross functionality are typically performed at the wafer level by probe testing. Burn-in tests and full functionality tests are typically performed after the dice have been singulated.
If the dice are packaged in a conventional plastic or ceramic package, the package provides an external lead system for testing. If the dice are to remain in an unpackaged condition, temporary packages may be required to house a single die for testing and to certify the die as a known good die (KGD). Some types of packaged dice, such as chip scale packages, can also require temporary packages for testing. U.S. Pat. No. 5,519,332 to Wood et al. discloses a representative temporary package for testing semiconductor dice.
One component of temporary packages for testing semiconductor dice functions as an electrical interconnect. The interconnect includes contact members for making temporary electrical connections with the dice. Typically, the contact members are configured to make electrical contact with corresponding contact locations on the dice, such as bond pads, test pads or fuse pads.
U.S. Pat. No. 5,483,741 to Akram et al. describes one type of interconnect for testing semiconductor dice. This type of interconnect includes a substrate, such as silicon, having integrally formed contact members. The contact members can be etched directly into the substrate and covered with a conductive layer. In addition, the interconnect includes conductors, such as deposited metal traces, for providing conductive paths to and from the contact members. One advantage of this type of interconnect is that the contact members can be formed in dense arrays using semiconductor fabrication processes. Since the contact members are formed integrally with the substrate, their location is fixed relative to the substrate and their CTE can match that of the substrate and a silicon die.
This type of interconnect functions satisfactorily for most types of testing. However, with advances in the architecture of semiconductor devices, it is advantageous to perform some testing of integrated circuits using very high speed testing signals. For example, testing frequencies of 500 MHz and greater are anticipated for some memory products such as DRAMS. The temporary packages and interconnects used to test dice must be capable of transmitting signals at these high speeds without generating parasitic inductance and cross coupling (i.e., “cross talk”).
One limitation of deposited metal conductors for interconnects is that the thickness of the metal conductors is limited by conventional deposition processes. Typically, CVD deposited metal conductors can be formed with a thickness of only about 2-3 μm. These thin conductors can be too resistive for high speed testing. The resistance can be lowered by widening the conductors but this greatly increases capacitance and causes speed delays.
Another limitation of deposited metal conductors for interconnects, is that low resistivity materials are sometimes difficult to utilize in conventional semiconductor fab shops. Copper, for example, is an unwanted contaminant for some semiconductor fabrication processes such as CVD and is preferable to avoid.
Another type of interconnect, as described in U.S. Pat. No. 5,487,999 to Farnworth, includes a rigid substrate such as silicon, but with contact members formed separately from the substrate. With this type of interconnect, the contact members can comprise metal microbumps mounted on a multi layered tape similar to TAB tape. The tape can also include conductors formed of copper foil or other highly conductive, relatively thick metal. The microbumps can be formed directly on the conductors or contained in vias formed in the tape.
Interconnects formed with microbump contact members and multi layered tape can include highly conductive conductors formed of copper foil or other relatively thick metal. However, during burn in testing temperature cycles of 200° C. or more can occur. The difference in the coefficients of thermal expansion (CTE) between the conductors and a substrate material such as silicon, can generate thermal stresses in the interconnect. In addition, thermal expansion can cause the conductors to shift relative to the substrate. If the contacts members are formed in direct contact with the conductors, movement of the conductors can displace the location of the contact members.
The present invention is directed to a hybrid interconnect having contact members formed integrally with the substrate but with conductors formed on a multi layered tape. The multi layered tape can be formed separately from the interconnect substrate and then bonded to the interconnect substrate with the conductors in electrical communication with the contact members. This allows low resistivity conductors to be used without requiring deposition of metals such as copper that can be detrimental to other semiconductor fabrication processes. In addition, with the present interconnect the location of the contact members can be fixed on the substrate while thermal stresses between the conductors and substrate can be absorbed by expansion joints.
In accordance with the invention, an improved interconnect for making electrical connections with a semiconductor die, a method for fabricating the interconnect, and a test system including the interconnect are provided. The interconnect includes a substrate with integrally formed contact members, and a pattern of conductors formed on a multi layered tape bonded to the substrate. The substrate can be silicon and the contact members formed in dense arrays using semiconductor fabrication processes, such as etching and metallization processes. The bonded tape provides improved electrical characteristics including lower resistivity and impedance matching of the conductors with testing circuitry.
The contact members extend above the conductors and are configured to electrically contact corresponding contact locations (e.g., bond pads) on the die. In the illustrative embodiment the contact members comprise raised pillars etched on the substrate and covered with conductive layers. The contact members can also include penetrating projections configured to penetrate the contact locations on the die to a limited penetration depth. The conductors are configured to provide electrical paths to and from the contact members for electrical signal transmission.
The multi layered tape can include a polymer film (e.g., polyimide) laminated with a pattern of metal conductors. Advantageously, the metal conductors can be formed of low resistance copper foil, or other highly conductive, relatively thick material. In addition, the tape can include a ground or voltage plane to allow an impedance of the conductors to match that of the testing apparatus or testing circuitry. Still further, an electrically insulating adhesive layer can be formed between the tape and the substrate. The adhesive layer and tape, in addition to providing electrical insulation, absorb thermal stresses generated by expansion of the conductors relative to the substrate.
For forming an electrical connection between the contact members and conductors, the conductors can be etched with patterns of openings that correspond to the patterns of contact members on the substrate. The contact members can be placed into the openings, extending above the conductors, and a conductive material placed in the gap therebetween. The conductive material can comprise a resilient conductive adhesive or a solder alloy. The conductive material in addition to forming an electrical path, also functions as an expansion joint, to accommodate thermal expansion of the conductors without stressing the contact members. The contact members can also include bases formed by stepped portions of the substrate. The bases raise the tips of the contact members with respect to the surface of the substrate, and facilitate formation of the electrical connections between the contact members and conductors.
A system for testing semiconductor dice can include a temporary package for containing the interconnect and a single unpackaged die. The temporary package can include a base and a force applying mechanism for biasing the die and interconnect together. The interconnect establishes temporary electrical communication with the die, and provides conductive paths to and from contact locations on the die to terminal contacts on the package base. The terminal contacts can be placed in electrical communication with a test apparatus such as a burn in board, configured to apply test signals to the integrated circuits on the die.
An alternate embodiment system can include an interconnect formed as a probe card configured for testing semiconductor dice contained on a wafer. The wafer can be an entire semiconductor wafer or portion of a wafer or other semiconducting substrate. A conventional testing apparatus such as a wafer probe handler can be used to support and bias the probe card and wafer together during the testing procedure.
The substrate 12 can be formed of a material such as silicon, silicon-on-glass, silicon-on-sapphire, germanium, ceramic, or photomachinable glass. In general, these materials are rigid and provide a good CTE match with a silicon die. The substrate 12 includes patterns of contact members 20 (
The contact members 20 (
As will be further explained, the contact members 20 (
The multi layered tape 14 (
The multi layered tape 14 can also include a ground or voltage plane formed of a metal layer (not shown) embedded in the polymer film 16 at a predetermined distance with respect to the conductors 18. This permits an impedance of the conductors 18 to be matched to an impedance of other electrical components of a testing system (e.g., testing circuitry).
An adhesive layer 24 (
The multi layered tape 14 can include patterns of openings 26 (
The conductive material 28 can be a conductive adhesive such as a metal filled epoxy (e.g., silver epoxy) or other material that is conductive in any direction. Alternately, the conductive material 28 can be an anisotropic conductive adhesive formed such that electrical resistance in one direction will differ from that measured in another direction. For example, X-axis and Z-axis anisotropic adhesives are filled with conductive particles to a low level such that the particles do not contact each other in selected planes. Curing is typically accomplished by compression of the adhesive along the direction of conduction.
The conductive material 28 can be formed as a viscous paste or as a film that is applied and then cured to harden. For example, conductive adhesives are commercially available in a thermal plastic, or thermal setting, paste or film. Thermal plastic conductive adhesives are heated to soften for use and then cooled for curing. Thermal setting conductive adhesives require heat curing at temperatures from 100-300° C. for from several minutes to an hour or more. Suitable conductive adhesives are sold under the trademarks: “X-POLY” and “Z-POXY”, by A.I. Technology, Trenton, N.J.; and “SHELL-ZAC”, by Sheldahl, Northfield, Minn. Conductive adhesives are also sold by 3M, St. Paul, Minn.
The conductive material 28 can be formed by deposition into the openings 26 (
In addition, with the conductive material 28 formed of a conductive adhesive, the material can be selected to provide a resilient expansion joint between the contact members 20 and conductors 18. With the contact members 20 formed of silicon and the conductors 18 formed of copper, the conductive material 28 allows the conductors 18 to shift without stressing and changing the location of the contact members 20. In a similar manner, the electrically insulating adhesive layer 24 (
As shown in
The height of the contact members 20 and the thickness of the multi layered tape 14 can be selected such that the contact members 20 extend above the surface of the conductors 18 and are free to contact the contact locations 21 (FIG. 3) on the die 22 without interference from the tape 14. By way of example and not limitation, the contact members 20 can be formed with a height of from 50-100 μm, a width of about 50-100 μm, and a spacing of about 50-100 μm. The conductors 18 for the multi layered tape 14 can be formed with a thickness of about 10-20 μm. The difference between the height of the contact members 20 and the thickness of the tape 14 is approximately equal to the distance between the tips of the contact members 20 and the surface of the conductors 18. The polymer film can be formed with a thickness of about 10-20 μm. The adhesive layer 24 can be formed with a thickness of about 5-20 μm. The openings 26 can be formed with a diameter of from about 60 to 100 μm.
As shown in
In addition, alignment fiducials 40 (
The contact member 20A can be formed by laser drilling, punching, etching or similarly forming, concave depressions in the substrate 12A. The conductive layer 32A can then be formed in the depressions using a suitable deposition process. The conductors 18A can also include an opening 33 formed by etching or other subtractive process. The conductive layer 32A and opening 33 can be sized and shaped to retain the bumped contact location. Conventionally formed solder bumps on a bumped die will have a diameter of from 5 mil to 30 mil. Accordingly, the concave depression in the substrate 12A and the opening 33 in the conductor 18A can be formed with diameters in this size range.
Initially, as shown in
The projections 30 can be elongated blades or sharp points formed in locations that match the placement of the contact locations 21 (
Once the projections 30 are formed, the hard mask can be stripped and another mask (not shown) can be formed for etching the substrate 12 to form the contact members 20. Using an anisotropic etch process, the contact members 20 can be formed as topographically elevated pillars generally conical in shape. A representative height of the contact members 20 from base to tip can be from 50-100 μm. The contact members 20 thus have a height that is from 50 to 1000 times greater than the height of the penetrating projections 30.
A representative width of each side of the contact members 20 can be from 40-80 μm. In use, the contact members 20 separate the substrate 12 from the die 22 (FIG. 3). This separation distance functions to clear particulate contaminants on the opposing surfaces that could cause shorting. The separation distance also functions to diminish cross talk between the die 22 and the substrate 12 during the test procedure. Following formation of the contact members 20, the etch mask can be stripped.
Suitable etch processes for forming the contact members 20 and projections 30 substantially as shown in
Following formation of the insulating layer 34 and as shown in
Following blanket deposition of the desired conductive metal, a resist mask can be formed and used for etching the conductive metal such that at least a portion of the contact members 20 remain covered with the conductive layers 32. The resist mask can be deposited using a standard photoresist deposition and exposure process. This can include spin deposition, followed by hardening, exposure and development. U.S. Pat. No. 5,607,818 incorporated herein by reference describes a method for patterning a conductive layer using an electrophoretically deposited layer of resist.
As an alternative to a metallization process (i.e., depositing resist, forming mask, etching), the conductive layers 32 can be formed as a metal silicide using a process as disclosed in U.S. Pat. No. 5,483,741 incorporated herein by reference.
An electrical connection between the conductors 18S on the multi layered tape 14S and the conductive layers 32S on the contact members 20S can be formed using a conductive adhesive as previously described, or with a solder bead 44. In addition, the conductors 18S for the multi layered tape 14S can overhang from an edge of a polymer film 16S to overlap the conductive layers 32S and facilitate formation of the solder beads 44. In this embodiment the conductors 18S and conductive layers 32S can be formed of a solder wettable metal. The solder bead 44 can comprise tin-lead or other solder alloy applied by wave soldering, reflowing or other process. For example, solder can be screen printed or electroplated in desired locations on the conductors 18S of the multi layered tape 14S. The tape 14S can then be applied to the substrate 12S and the solder reflowed.
The temporary package 50 includes a package base 52 (
The force applying mechanism 54 secures the die 22 to the package base 52 and presses the die 22 against the interconnect 10. The force applying mechanism 54 includes a cover 56 (
Further details of the temporary package 50 are disclosed in U.S. patent application Ser. No. 08/580,687 incorporated herein by reference. The cited patent application also describes a method for optically aligning the contact members 20 (
For testing the die 22, the terminal contacts 72 on the temporary package 50 can be placed in electrical communication with testing circuitry 74 (FIG. 9C). For example, the temporary package 50 can be placed on a burn in board or other testing apparatus in electrical communication with the testing circuitry 74. Test signals can then be applied through the terminal contacts 72 on the temporary package 50, and through the contact members 20 (
Thus an improved interconnect 10 (
Still further, because the conductors 18 (
As shown in
In addition, the wafer probe handler 82 includes a force applying mechanism 86 and a force applying member 88. The force applying member 88 presses against a pressure plate 90 and a compressible member 92 in contact with a backside of the probe card 80. The compressible member 92 can be formed of an elastomeric material, such as silicone, or as a gas filled bladder. The compressible member 92 cushions the forces applied to the wafer 78 and allows the probe card 80 to self planarize to the wafer 78. The wafer probe handler 82 can also include a chuck (not shown) for supporting the wafer 78. Suitable wafer probe handlers 82 are commercially available from Electroglass and others.
While the invention has been described with reference to certain preferred embodiments, as will be apparent to those skilled in the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims.
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|U.S. Classification||324/756.05, 324/762.04|
|International Classification||G01R1/04, G01R1/073, G01R31/02|
|Cooperative Classification||G01R1/0735, G01R1/0466|
|European Classification||G01R1/04S3D3, G01R1/073B6|
|Oct 21, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Jan 3, 2014||REMI||Maintenance fee reminder mailed|
|May 23, 2014||LAPS||Lapse for failure to pay maintenance fees|
|Jul 15, 2014||FP||Expired due to failure to pay maintenance fee|
Effective date: 20140523